In recent years, mobile terminals such as notebook computers, cellular phones, and personal digital assistants (PDAs) are increasingly widespread. As secondary batteries used as a power source for these mobile terminals, lithium ion secondary batteries are frequently used.
In the lithium ion secondary battery, a separator is generally provided to prevent short circuit between a positive electrode and a negative electrode. This separator may be provided with a porous membrane on a separator substrate, if necessary. As an example of such a porous membrane, there has been known a membrane including non-conductive particles such as alumina, and a binder that binds the non-conductive particles. There has also been proposed to provide the aforementioned porous membrane on an electrode plate of an electrode (see Patent Literatures 1 and 2).
In addition, techniques in Patent Literatures 3 to 9 have also been known.